The term monolayer refers to solid materials of minimum thickness. Occasionally, it is only a single layer of atoms thick; in crystals it can be three or more layers. Experts also speak of two-dimensional materials. In this form, they frequently exhibit unexpected properties that make them interesting for research. The so-called transition metal dichalcogenides (TMDC) are particularly promising. They behave like semiconductors and can be used to manufacture ultra-small and energy-efficient chips, for example.